By focusing on one component of the central nervous system (i.e., the ACh-receptors), the objective is to study their interactions with different drugs (e.g., cholinergic, adrenergic, serotonergic, histaminergic, dopaminergic, tranquilizers, antidepressants, stimulants, hallucinogens). It is essential to do the study on pure ACh-receptors so as to eliminate interferences by other macromolecules. It is hoped that information will be gained on whether these receptors act as targets (primary or secondary) for drugs other than the known cholinergic receptor drugs. This will add to our understanding of the mode of action and side effects of these drugs. Initially, fractions containing synaptic membranes will be prepared from whole and parts of the vertebrate brain, and using equilibrium dialysis, the nicotinic and muscarinic receptors will be identified by their specific binding of 3H-nicotine and 3H-pilocarpine, or 3H-QNB, respectively. A preliminary screening of the various drugs will be performed to identify the ones that bind to ACh-receptors. The receptors will be solubilized, then purified primarily by affinity chromatography. Using equilibrium dialysis, binding of ACh to the purified nicotinic and muscarinic receptors will be studied in detail, and the effect of drugs on the binding and subunit interactions will be determined as well as the competitive, noncompetitive or allosteric nature of the drug effect on ACh-binding. The pure receptor proteins will be used as antigens to produce antibodies, which will be radiolabeled. By means of autoradiography, the ACh-receptors can be localized in the brain and the cholinergic pathways mapped, pointing to the possible target areas for some of these drugs. BIBLIOGRAPHIC REFERENCE: Eldefrawi, M. E. and Eldefrawi, A. T. (1977) Acetylcholine receptors. In "Receptors and Recognition" (P. Cuatrecasas and M. F. Greaves) Ser. A, 4.